How about Angelina Jolie? Her usual accent is pretty nasty, but when she puts on the upper-class English accent (ala Lara Croft) she sounds lovely (she's still pretty rough, though). As for singing, then it's got to be Hayley Williams. Have a listen to some of the unplugged / live stuff she's done; serious eargasm material.
The best Male voices are Patrick Stewart and Rowan Williams!
Northwind - Member
Shireen Liane of the Slingbacks/Lumiere Brothers. Can't find the best example online, so here's a halfassed one
Bloody hell, I didn't think anyone knew about The Slingbacks! Great band.
Voices, eh? Sandy Denny, Emmylou Harris, Shawn Colvin, Patty Griffin are all huge favourites of mine, Emmylou in particular, has a yearning quality to her voice that always raises the hair on the back of my neck, and sends shivers down my back.
There's another singer/songwriter who has a fantastic voice, mellifluous is the word that springs to mind.
Her name's Kris Delmhorst, and she's wonderful!
A personal favourite song of hers is You're No Train from her album Song For A Hurricane
I advise anyone who treasures a good voice along with quality songwriting to check her out.